There is a lot of chatter going on in the last couple of days about Elune. Why she did this, why she didn't do that, why she let this happen, etc.
My question though, what do we actually know about Elune? What are the explicit powers that we have seen or know about?
We know she was responsible for Ysera going to Ardenweald
We know she granted Tyrandae the powers of the Night Warrior
[I believe] there was a Satyr in Legion that came to regret their life and wanted to return to a Night Elf and I believe Elune granted that wish [could be mis-remembering this one]
Is that it? There has to be others I am not remembering.
Elune has been a largely absent figure in all of WoW. Perhaps I am missing other expressions of Elunes power, but perhaps the simple answer to why didn't Elune stop Sylvanus was simply because she couldn't. She doesn't have that power. We already know Elune isn't All-Knowing, as she didn't know all the souls were going to the Maw. Her connection to the Winterqueen may have been enough to let her know there was a soul shortage. She didn't have the power to stop Sylvanus, but she could help some of their suffering and [thought] she could ensure their resting place in Ardenweald.